Various optical deflectors which deflect incident light have conventionally been studied. Optical deflectors are devices indispensable to, for example, laser scanners used in laser printers or the like. Examples of conventional optical deflectors include polygon scanners, galvanometer scanners, and MEMS mirrors. However, since such polygon scanners, galvanometer scanners, MEMS mirrors, or the like include a mobile unit (mechanical mechanism) for moving parts, there is a problem in that a failure easily occurs. For this reason, there is demand for the development of optical deflectors capable of deflecting light without including a mobile unit.
In response to that demand, an optical deflector as disclosed in Patent Literature (PTL) 1 below has been proposed. This optical deflector does not include a mobile unit, and deflects light with use of the fact that the refractive indexes of liquid crystals are modulated by application of voltage. Through this, it is possible to reduce the occurrence of failures and achieve high reliability.
Now, a conventional optical deflector will be described with reference to FIGS. 14A and 14B. FIG. 14A is a cross-sectional view of a conventional optical deflector, and FIG. 14B is a cross-sectional view of the optical deflector taken along line A-A in FIG. 14A. An optical deflector 50 shown in FIGS. 14A and 14B includes an optical deflection element 501 and three pairs of electrodes 502a, 502b, and 502c provided in the periphery of the optical deflection element 501. The optical deflection element 501 includes a liquid crystal 503 having a triangular shape in cross section and a dielectric 504 having a shape complementary to that of the liquid crystal 503. The dielectric 504 is provided on the inclined face side of the liquid crystal 503, as a result of which the optical deflection element 501 as a whole is configured in a rectangular shape in cross section. The dielectric 504 may be made of, for example, a polymeric resin such as a plastic, or glass. The three pairs of electrodes 502a, 502b, and 502c are each provided such that the two electrodes face each other with the optical deflection element 501 therebetween.
Light is incident on the optical deflection element 501 as indicated by an arrow 505 in FIG. 14A. The refractive index of the liquid crystal 503 is modulated by application of voltage (including zero voltage) between each of the three pairs of electrodes 502a, 502b, and 502c, and the light incident on the optical deflection element 501 is deflected. When a refractive index NL of the liquid crystal 503 is higher than a refractive index ND of the dielectric 504, light is refracted in a direction indicated by an arrow 505h in FIG. 14A. When the refractive index NL of the liquid crystal 503 is lower than the refractive index ND of the dielectric 504, light is refracted in a direction indicated by an arrow 505m in FIG. 14A. In this way, the light deflected inside the optical deflection element 501 is emitted from the optical deflection element 501. When the refractive index NL of the liquid crystal 503 and the refractive index ND of the dielectric 504 are the same value, light travels in a straight direction indicated by an arrow 505s in FIG. 14A without being refracted.
The response speed of the optical deflection element 501 when deflecting light depends on the height of the liquid crystal 503. According to PTL 1, the liquid crystal 503 having a height of 20 μm or less achieves a response speed of 100 μsec or less, and the liquid crystal 503 having a height of 15 μm or less achieves a response speed of 30 μsec or less. Here, by changing the difference between the refractive index NL of the liquid crystal 503 and the refractive index ND of the dielectric 504 by approximately 0.2, light can be deflected at an angle of approximately 30 degrees.
Furthermore, PTL 2 below discloses a liquid crystal display apparatus which provides three dimensional (3D) images using the above optical deflector. FIG. 14C is a cross-sectional view of a conventional liquid crystal display apparatus. A liquid crystal display apparatus 60 in FIG. 14C includes an optical deflector 601, a light guide plate 602, a light source 603, a liquid crystal panel 604, a pair of stereo cameras 605a and 605b, and a control unit 606. The optical deflector 601 includes a plurality of the optical deflection elements 501 arranged horizontally. The control unit 606 controls the liquid crystal panel 604, the optical deflector 601, the light source 603, and the pair of stereo cameras 605a, and 605b. Light emitted from the light source 603 is incident on the lateral face of the light guide plate 602, propagates through the light guide plate 602, is directed upward in a substantially vertical direction by the prism shaped bottom of the light guide plate 602, and then is emitted from the top face of the light guide plate 602. The light, incident on the optical deflector 601 substantially vertically, is deflected at a different deflection angle for each optical deflection element 501 at predetermined timing, thereby being collected onto a right eye 607a of a viewer 607. In synchronization with the predetermined timing, the control unit 606 causes the liquid crystal panel 604 to display a right-eye image. After the above predetermined timing, light is deflected by the optical deflector 601 to be collected onto a left eye 607b of the viewer 607. In synchronization with this timing, the control unit 606 causes the liquid crystal panel 604 to display a left-eye image. By alternately switching between the images displayed on the liquid crystal panel 604 at a predetermined cycle (for example, 8.3 msec: 120 Hz), the viewer 607 perceives the images displayed on the liquid crystal panel 604 as 3D images.
In a case where the position of the viewer 607 shifts, the control unit 606 adjusts the angle of light deflected the deflector 601, based on the positions of the eyes 607a and 607b of the viewer 607 detected by the pair of stereo cameras 605a and 605b. As a result, it is possible to continuously provide right-eye images to the right eye 607a and left-eye images to the left eye 607b. 